1. Field of the Invention
The present invention relates to a method for manufacturing a wired circuit board and, more particularly, to a method for manufacturing a wired circuit board comprising the step for forming a coverlay on a wired circuit board formed in an elongated film form.
2. Description of the Prior Art
Generally, wired circuit boards, including a flexible wired circuit board, each comprises a specified wired circuit pattern of a metal foil formed on an insulating film and a coverlay of resin formed on the wired circuit pattern to cover it.
In the manufacturing method of a wired circuit board, the coverlay is generally formed, for example, by solution of thermosetting resin being continuously applied to a specified wired circuit pattern formed on the insulating film of an elongate wired circuit board, first, and then dried, or by an uncured thermosetting resin film being continuously laminated on the specified wired circuit pattern and then the uncured thermosetting resin being cured.
The curing of the thermosetting resin requires a heat treatment. The heat treatment is generally carried out by using feed rolls, a winding roll and a heating furnace provided between the feed rolls and the winding roll. The thermosetting resin on the wired circuit board is heated to be cured by the heating furnace by the time the wired circuit board, after fed from the feed roll, is wound up by the winding roll.
This conventional method involves the problem that since tension is exerted on the wired circuit board when wound up by the winding roll and also elasticity modulus of the insulating film forming the wired circuit board is reduced by heat, the insulating film is increased in length and is changed in dimension. This dimensional change significantly affects on fine pitch of the wired circuit board which has been increasingly demanded in recent years.
To prevent this problem, it is conceivable, for example, that the wired circuit board is heated in its rolled state. However, since the uncured thermosetting resin usually softens and flows when heated, there is the possibility that when heated, the uncured thermosetting resin may contact with the wired circuit board which is wound over it. If this is the case, the pattern on the wired circuit board may be transferred to the contact surface to impair the formation of the coverlay formed.